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Download Human Genetic Disorders
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Human Genetic Disorders A genetic disorder is an abnormal condition that a person inherits through genes or chromosomes. Genetic disorders are caused by mutations, or changes in a person’s DNA. Human Genes and Mutations • Mutations happen when an error occurs while copying the DNA sequence • Not all mutations are harmful, some are beneficial and others have no effect at all • Certain chemicals, x-rays and radioactive substances can cause mutations Chromosome Disorders • Individual, or point, mutations can occur, but an error can occur with the number of chromosomes that should be inherited • These mistakes usually occur in meiosis – Chromosome number is too many or too few – Results from Non-disjucntion • An incorrect number of chomosomes is often fatal to an unborn embryo or fetus, or the baby dies shortly after birth – Down Syndrome-3 copies of Chromosome #21 Common Genetic Disorders • Cystic Fibrosis – Body produces abnormally thick mucus in the lungs and intestines that can lead to bacterial infections – Causes difficulty breathing and digesting – It is a recessive allele (both parents must carry it) and has no known cure • Sickle-cell disease (Sickle-cell Anemia) – Caused by abnormal hemoglobin (protein that carries oxygen) causing pain and weakness – The allele for it is co-dominant. – People with two sickle cell alleles have it – People with one sickle-cell allele produce both normal and abnormal hemoglobin but don’t usually have symptoms. There are treatments but no cure. Common Genetic Disorders cont. • Hemophilia – Disorder that causes the blood to clot slowly or not at all. One of the proteins needed for normal clotting is not produced. – It is caused by a recessive allele on the X chromosome and thus is sex-linked. – Occurs more often in males than females. – Can develop after birth but usually genetic. – http://www.sciencecases.org/hemo/hemo.asp • Down Syndrome – Due to an extra copy of chromosome 21 – Occurs when chromosomes fail to separate during meiosis – Down Syndrome patients have a distinct appearance and some degree of mental retardation but many lead full active lives Modern Approach to Genetic Disorders • Doctors can detect genetic disorders using amniocentesis and karyotypes • Amniocentesis: chromosomes from fluid surrounding the baby are examined • Karyotype: a picture of the chromosomes revealing whether the baby has the right number or whether it is a boy or girl • Couples with family histories of disorders must weigh the chances of children having a disorder. Karyotypes, pedigrees and Punnett squares can help with determining the potential risks